The footnotes set forth hereinbelow are listed in detail at the end hereof.
The study of tendon and ligament injury, and the subsequent treatment of such injuries, has led to numerous techniques for the repair, augmentation, or replacement of this injured tissue. Numerous techniques have called for the use of naturally occurring materials (such as autografts allografts, and xenografts, or synthetic materials (for example, carbon fibers, DACRON, or other polymers. However, many investigators have stated that no one technique can be called ideal. The repair of tendon and ligament injury is difficult at best, and these technical problems lead to prolonged recovery periods (often greater than one year), painful rehabilitation, and possibly impairment of function; for example, inadequate repair of the anterior cruciate ligament results in degenerative changes to the knee, possibly leading to arthritic conditions.
The complete replacement of ligaments has been a challenging materials problem, as the materials must (1) be biocompatible; (2) have sufficient mechanical strength; (3) have resilience to withstand millions of fatigue cycles associated with normal ligament use; (4) withstand the biochemical and physiological environment; and (5) support the growth of new connective tissue. To date, several synthetic materials have been found to be biocompatible and to support fibroblast growth to some extent however, synthetic materials have demonstrated a susceptibility to stretching, fatigue, and shear and other stresses that lead to device failure. Naturally occurring collagenous material, such as autografts, allografts, or xenografts, also have limitations. Ligament repair with autogenous tissue has been used successfully for many years, but its use is not always possible, especially when trauma or disease is severe.
In addition, histological studies of autogenous grafts indicate an ischemic necrosis followed by revascularization and remodeling; during the ischemic and revascularization stages, the mechanical strength of the graft is diminished. Allograft supply has become a major problem, along with prevention of viral contamination, and recent data suggest that revascularization and remodeling do not occur, resulting in graft deterioration. Several research teams have reported the use of xenografts for ligament repair; however, poor experience with fixed xenografts has significantly discouraged investigators from pursuing this option.
One concept followed by several investigators is the augmentation of an autogenous graft, as opposed to complete replacement, providing temporary mechanical integrity until new tissue can assume the normal mechanical function.
The initial strength of a polymer-coated carbon fiber used to augment the iliotibial band graft exceeded that of normal tendon or ligament, and the carbon fiber became intertwined with new connective tissue as healing proceeded. Other materials, including polypropylene, have been used for augmentation of patellar tendon grafts in ligament reconstruction.
An important objective of this invention is to provide a collagen bound fabric which is used in a novel ligament repair device incorporating several key concepts; (1) the mechanical characteristics of the device will mimic those of the natural ligament and will initially be equal to or greater than normal connective tissue; (2) the surface of the implant will serve as a matrix for new tissue; (3) the femoral and tibial attachment site of the ligament prosthesis will encourage bony ingrowth; and (4) the ligament prosthesis design will take into account varying tension modes as a function of knee extension.
DACRON has been studied extensively as a possible material for the repair of tendon and ligament, and its chemical properties are well documented. DACRON was found to have low reactivity when used in intraarticular procedures. Commercial DACRON vascular grafts have been found to maintain strength for over two years. However, DACRON has been found to be subject to shear or laceration in the canine stifle joint, and the material loses tensile strength over time. It has been noted previously that fibrous tissue ingrowth to DACRON and other synthetics minimizes the internal abrasive forces, and thus decreases failure due to shear or laceration. The use of a collagen surface will enhance the growth and strength of the new fibrous tissue and therefore decrease the recovery time.